1. Technical Field
This invention relates to an elevator system and, more particularly, to a compensating rope sheave tie down.
2. Background Art
A conventional elevator system comprises an elevator car suspended on one end of a hoist rope in a hoistway with a counterweight suspended on the other end of the hoist rope. A compensating rope is hung from the underside of the elevator car to the underside of the counterweight to balance the weight of the hoist rope as the car and counterweight move alternatingly up and down within the hoistway. A compensating rope sheave disposed on the bottom of the hoistway allows the compensating rope to pass therethrough. The sheave travels a relatively short distance vertically along a set of guide rails to accommodate for expansion and contraction of the ropes resulting from changing weather conditions.
Typical elevator systems also include a tie down of the compensating rope sheave, wherein the tie down serves two functions. One function is to allow the sheave to move slowly within the limits of the guide rails to accommodate for the weather changes. The other function of the tie down is to prevent the sheave from sudden upward movement if the elevator car suddenly jumps upward. Thus, if the elevator car suddenly moves upward, subsequently pulling the compensating rope sheave upward, the tie down would hold the compensating sheave down. As a result, the tie down would stop the elevator car from further upward movement, since the compensating rope will be retained by the sheave and will not be able to travel upward.
Typical kinds of tie downs currently employed in the industry are either a ratchet and pawl type system or a hydraulic system. The conventional ratchet and pawl type system may jam and stop the vertical motion of the compensating sheave. The hydraulic system is very complex and expensive.